Method and processor for obtaining moments and torques in a biped walking system

ABSTRACT

A method and processor for obtaining torques to be applied to joints of a leg of a biped walking system are provided. The method comprises the steps of obtaining moments acting around the joints of the leg, using the vertical component of the ground reaction force acting on the leg at the point of application of the ground reaction force, the vertical components of forces acting on the joints of the leg and a term of the acceleration of gravity and without using the horizontal components of the forces acting on the joints of the leg and a term of acceleration except the term of the acceleration of gravity and obtaining the torques to be applied to the joints of the leg, based on the moments acting around the joints of the leg. The vertical component of the ground reaction force acting on the leg, is obtained based on which leg or legs are in contact with the ground. The processor is configured to perform the above steps.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of U.S. provisional applicationsNo. 60/413,024 filed on Sep. 23, 2002 and No. 60/421,964 filed on Oct.28, 2002.

FIELD OF THE INVENTION

[0002] The present invention relates to a method for obtaining momentsacting on joints of legs of biped walking system such as biped walkingrobots. The present invention further relates to a method for obtainingtorques to be given to joints of legs.

BACKGOUND OF THE INVENTION

[0003] It is required to obtain ground reaction forces acting on legs ofa biped walking system and then based on the ground reaction forces toobtain moments acting on joints of the legs of the biped walking system,in control of human assist systems and in control of movement of bipedwalking robots. Such human assist systems are intended to assist humanoperations against gravity including going up and down stairs, sittingand standing up, squatting, and moving up and down with heavy load.Based on data including the obtained moments, assist torques for humanassist systems or a target driving torque for each joint of bipedwalking robots can be determined.

[0004] Japanese Patent Application Unexamined Publication (KOKAI) No.2000-249570 discloses a method for obtaining ground reaction forces. Inthis technique, ground reaction forces acting on legs are obtained as alinear combination of trigonometric functions having different periodsof 1/n (n=1, 2, . . . ) of a walking period, because waveformsrepresenting temporal changes in ground reaction forces acting on legs,periodically change while a biped walking system is normally walking. Inthis case, as weighting factors of respective trigonometric functionsfor the combination, fixed values predetermined for each biped walkingsystem or those obtained by adjusting the fixed values according togeographic features, are employed.

[0005] However, in the above technique, ground reaction forces acting onlegs are obtained for a step or steps of biped walking systems andtherefore accurate ground reaction forces can hardly be obtained in sucha case as walking manner of biped walking systems successively changes.Further, for higher accuracy of ground reaction forces to be obtained,weighting factors of trigonometric functions must be set for each bipedwalking system and must be adjusted according geographic features. So,it is very difficult to obtain accurate ground reaction forces withoutbeing affected by environment where biped walking systems move and byindividual variation of biped walking systems.

[0006] U.S. Pat. No. 6,152,890 discloses an apparatus and a method tomeasure load of working persons. However, the apparatus and method donot enable accurate measurement of torques acting on the joints.

[0007] As to biped waking robots, for example, a method is known, inwhich sensors such as 6-axis force sensors are set to ankles or feet ofthe robots to obtain ground reaction forces. Further, another method isknown in which biped walking systems are made to walk on a force plateon the floor to obtain ground reaction forces based on outputs of theforce plate.

[0008] However, in techniques using force sensors, it is necessary toattach force sensors to ankles and feet of a person in order to obtainground reaction forces acting on the legs of the person. Such forcesensors hinder the person from walking in his or her daily life.Further, in techniques using a force plate, ground reaction forces canbe obtained only under an environment in which the force plate has beeninstalled.

[0009] In conventional human assist systems, differential operations areused to obtain moments on joints of legs and the differential operationscause noises of moments on joints of legs. Additionally, horizontalcomponents of forces are used to obtain moments on joints of legs. Sincehorizontal forces, or accelerations are hard to measure, measuredhorizontal forces cause errors in moments on joints of legs. Further,many acceleration terms must be obtained. Accordingly, huge amount ofdifferential operations might restrict real-time processing.

[0010] Under the situation mentioned above, there is a great need for asimpler joint moment estimation method by which moments acting on jointsof legs can be obtained accurately and in real time, particularly forpersons as biped walking systems.

[0011] Additionally, there is a great need for a real-time and robustcontrol method of biped walking systems by which torques such as assisttorques applied to joints of legs in human assist systems or the like,can be obtained.

SUMMARY OF THE INVENTION

[0012] First, the basic idea of an estimation method of ground reactionforces, used in joint moment estimation method for biped walking systemsof the present invention, will be described below.

[0013] Motions of biped walking systems, for example, motions of legs inwalking, include a single-support phase in which one of the legs (2, 2)of a biped walking system is in contact with the ground as shown in FIG.1 (a) and a double-support phase in which both of the legs (2, 2) are incontact with the ground as shown in FIG. 1 (b).

[0014] In a single-support phase, the equation of (translational) motionof the center of gravity of the biped walking system in the absolutecoordinate system fixed to the ground on which the biped walking systemmoves, represents such a relationship as below. That is, therelationship is that a product of an acceleration of the center ofgravity and a weight (mass) of the biped walking system equals theresultant of gravity (a product of the weight of the biped walkingsystem and the acceleration of gravity) and the ground reaction forceacting on the leg in contact with the ground.

[0015] More specifically, if component in the X direction (thehorizontal direction in which the biped walking system (1) moves) andthat in the Z direction (the vertical direction) of acceleration a ofthe center of gravity G0 of the biped walking system, are represented asax and az and component in the X direction and that in the Z directionof the ground reaction force F are represented as Fx and Fz, as shown inFIG. 1 (a), the equation of motion of the center of gravity G0 isrepresented as below.

^(T)(Fx, F z−M·g)=M· ^(T) (a x, a z)  (1)

[0016] where M is a weight of the biped walking system and g is theacceleration of gravity.

[0017] In both sides of Equation (1), ^(T)( , ) represents atwo-component vector. Hereinafter, a notation in the form of ^(T)( , )represents a vector.

[0018] Provided that a term of acceleration except a term of theacceleration of gravity, is negligible, the following equation can beobtained for the vertical component F z of a ground reaction force.

F z=M·(a z+g)  (2)

[0019] In this case, the weight M required to obtain an estimated valueof the ground reaction force F can be previously obtained by measurementor the like.

[0020] In a double-support phase, the equation of (translational) motionof the center of gravity of the biped walking system, represents such arelationship as below. That is, the relationship is that a product of anacceleration of the center of gravity and a weight of the biped walkingsystem equals the resultant of gravity (a product of the weight of thebiped walking system and the acceleration of gravity) and two groundreaction forces acting on the both legs. The two ground reaction forcesact respectively on the both legs at portions in contact with the floor.More specifically, if X and Z components of ground reaction force Ffacting on the leg (2) in the front in the direction of travel arerepresented as Ffx and Ffz and the X and Z components of ground reactionforce Fr acting on the leg (2) in the rear are represented as Frx andFrz, the equation of motion of the center of gravity can be representedas below.

^(T)(F fx+F rx, F fz+F rz−M·g)=M· ^(T)(a x, a z)  (3)

[0021] where ax, az, M and g in Equation (3) are described above.

[0022] Provided that a term of acceleration except a term of theacceleration of gravity, is regarded as negligible and the both legsbear an equal amount of gravity, the following equation can be obtained.

F fz=F rz=(½)·M·g  (4)

[0023] Accordingly, estimated values of the vertical components Ffz andFrz of a ground reaction force of each of the legs can be obtained bysubstituting a value of weight M of the biped walking system and a valueof the acceleration of gravity g into Equation (4).

[0024] In this case, the weight M required to obtain estimated values ofthe vertical components Ffz and Frz can be previously obtained bymeasurement or the like.

[0025] If terms of accelerations except terms of the acceleration ofgravity and terms of the horizontal components of forces are regarded asbeing negligible, the vertical components of forces and moments actingon the knee joints of the legs can be obtained as below. They areobtained based on the vertical components of the ground reaction forcesobtained in such a way as mentioned above, points of application of theground reaction forces obtained based on attitude of the legs and thelike and terms of the acceleration of gravity. The vertical componentsof forces and moments acting on the hip joint can be obtained based onthe vertical components of forces and moments acting on the knee jointsof the legs and the term of the acceleration of gravity. Further, basedon moments acting on the knee joints and the hip joint of the legs,torques such as assist torques to be applied to the knee joints and thehip joint of the legs in human assist systems, can be obtained. Thus,control of human assist systems for assisting human operations can berealized.

[0026] Based on the above description, the present invention will bedescribed below. A method for obtaining torques to be applied to jointsof a leg of a biped walking system, according to the present inventioncomprises the step of determining which leg or legs are in contact withthe ground. The method further comprises the steps of obtaining thevertical component of a ground reaction force acting on the leg, basedon which leg or legs are in contact with the ground and obtaining apoint of application of the ground reaction force. The method furthercomprises the step of obtaining moments acting around the joints of theleg, using the vertical component of the ground reaction force acting onthe leg at the point of application of the ground reaction force, thevertical components of forces acting on the joints of the leg and a termof the acceleration of gravity and without using the horizontalcomponents of the forces acting on the joints of the leg and a term ofacceleration except the term of the acceleration of gravity. The methodfurther comprises the step of obtaining the torques to be applied to thejoints of the leg, based on the moments acting around the joints of theleg.

[0027] Thus, in the present invention, the vertical components alone offorces acting on the legs are used and the horizontal components are notused. Accordingly, errors in measurement of forces in the horizontaldirection, that is, accelerations in the horizontal direction do notcause errors in joint moments. Further, as forces in the verticaldirection, forces caused by gravity alone are used. Accordingly, errorsin measurement of forces in the vertical direction do not cause errorsin joint moments.

[0028] Further, since the present invention does not need anacceleration of each portion of the leg except the acceleration ofgravity, noises are reduced and an operation speed is increased.Accordingly, robust and real-time operations can be easily achieved inobtaining moments acting around joints of the legs of the biped walkingsystem.

[0029] According to an embodiment of the present invention, in asingle-support mode the vertical component of the ground reaction forceacting on the leg is assumed to be M·g and in a double-support mode thevertical component of the ground reaction force acting on each of thelegs is assumed to be (½)·M·g, where M is a weight of a person and g isthe acceleration of gravity. Accordingly, the vertical component of theground reaction force acting on the leg or legs can be easily obtained,and robust and real-time operations can be still easily achieved.

[0030] According to an embodiment of the present invention, in the stepof determining which leg or legs are in contact with the ground, thedetermination is made based on a value of the vertical component ofacceleration measured on the body. Thus, complicated processes for thedetermination are not required and therefore an operation speed isfurther increased. Accordingly, real-time operations can be still easilyachieved in control of human assist systems for assisting humanoperations and the like.

[0031] According to another embodiment of the present invention, in thestep of determining which leg or legs are in contact with the ground,the determination is made using a sensor. Thus, operations for thedetermination are not required and therefore real-time operations can bestill easily achieved in control of human assist systems for assistinghuman operations and the like. Further, the determination is made withreliability based on the simple sensor.

[0032] According to another embodiment of the present invention, in thestep of obtaining a point of application of the ground reaction force,the point is obtained based on the attitude of the leg and a location ofthe center of gravity of the body. Accordingly, robust operations can beachieved with a simple method.

[0033] According to another embodiment of the present invention, in thestep of obtaining a point of application of the ground reaction force,the point is obtained further using information from a sensor.Accordingly, the point is obtained with reliability based on informationform the sensor.

[0034] According to another embodiment of the present invention, in thestep of obtaining moments acting around the joints of the leg, at firstthe vertical component of a force acting on and a moment acting aroundthe knee joint of the shin, are obtained using the vertical component ofthe ground reaction force acting on the shin at the point of applicationof the ground reaction force and a term of the acceleration of gravityand without using the horizontal component of the ground reaction forceand a term of acceleration except the term of the acceleration ofgravity. Then the vertical component of a force acting on and a momentacting around the hip joint of the thigh, are obtained using thevertical component of a force acting on and a moment acting around theknee joint of the thigh and a term of the acceleration of gravity andwithout using the horizontal component of the horizontal component ofthe force acting on the knee joint and a term of acceleration except theterm of the acceleration of gravity.

[0035] Accordingly, a moment acting around the knee joint of the shinand a moment acting around the hip joint of the thigh can be obtainedwith reliability, using the ground reaction force acting on the leg atthe point of application of the ground reaction force and a term of theacceleration of gravity alone.

[0036] A method for obtaining moments acting around joints of a leg of abiped walking system, according to the present invention comprises thestep of determining which leg or legs are in contact with the ground.The method further comprises the steps of obtaining the verticalcomponent of a ground reaction force acting on the leg, based on whichleg or legs are in contact with the ground and obtaining a point ofapplication of the ground reaction force. The method further comprisesthe step of obtaining moments acting around the joints of the leg, usingthe vertical component of the ground reaction force acting on the leg atthe point of application of the ground reaction force, the verticalcomponents of forces acting on the joints of the leg and a term of theacceleration of gravity and without using the horizontal components ofthe forces acting on the joints of the leg and a term of accelerationexcept the term of the acceleration of gravity.

[0037] Thus, in the present invention, the vertical components alone offorces acting on the legs are used and the horizontal components are notused. Accordingly, errors in measurement of forces in the horizontaldirection, that is, accelerations in the horizontal direction do notcause errors in joint moments. Further, as forces in the verticaldirection, forces caused by gravity alone are used. Accordingly, errorsin measurement of forces in the vertical direction do not cause errorsin joint moments.

[0038] Further, since the present invention does not need anacceleration of each portion of the leg, noises are reduced and anoperation speed is increased. Accordingly, robust and real-timeoperations can be easily achieved in obtaining moments acting aroundjoints of the legs of the biped walking system.

[0039] A processor for obtaining torques to be applied to joints of aleg of a biped walking system, according to the present invention, isoperable in association with angular sensors on the joints and at leastone sensor set on the body of the biped walking system. The processor isconfigured to perform the following steps. The steps include determiningwhich leg or legs are in contact with the ground, using information fromthe at least one sensor set on the body and obtaining an attitude of theleg, using information from the angular sensors. The steps furtherinclude obtaining a location of the center of gravity of the whole bodyincluding the leg and obtaining the vertical component of a groundreaction force acting on the leg, based on which leg or legs are incontact with the ground. The steps further include obtaining a point ofapplication of the ground reaction force, using the attitude of the legand the location of the center of gravity of the whole body. The stepsfurther include obtaining moments acting around the joints of the leg,using the vertical component of the ground reaction force acting on theleg at the point of application of the ground reaction force, thevertical components of forces acting on the joints of the leg and a termof the acceleration of gravity and without using the horizontalcomponents of the forces acting on the joints of the leg and a term ofacceleration except the term of the acceleration of gravity. The stepsfurther include obtaining the torques to be applied to the joints of theleg, based on the moments acting around the joints of the leg.

[0040] A processor for obtaining torques to be applied to joints of aleg of a biped walking system, according to the present invention, isoperable in association with angular sensors on the joints, at least onesensor set on the body of the biped walking system and at least onesensor set on the leg. The processor is configured to perform thefollowing steps. The steps include determining which leg or legs are incontact with the ground, using information from the at least one sensorset on the leg and obtaining an attitude of the leg, using informationfrom the angular sensors. The steps further include obtaining a locationof the center of gravity of the whole body including the leg, andobtaining the vertical component of a ground reaction force acting onthe leg, based on which leg or legs are in contact with the ground. Thesteps further include obtaining a point of application of the groundreaction force, using the attitude of the leg and the location of thecenter of gravity of the whole body. The steps further include obtainingmoments acting around the joints of the leg, using the verticalcomponent of the ground reaction force acting on the leg at the point ofapplication of the ground reaction force, the vertical components offorces acting on the joints of the leg and a term of the acceleration ofgravity and without using the horizontal components of the forces actingon the joints of the leg and a term of acceleration except the term ofthe acceleration of gravity. The steps further include obtaining thetorques to be applied to the joints of the leg, based on the momentsacting around the joints of the leg.

[0041] Thus, in the present invention, the vertical components alone offorces acting on the legs are used and the horizontal components are notused. Accordingly, errors in measurement of forces in the horizontaldirection, that is, accelerations in the horizontal direction do notcause errors in joint moments. Further, as forces in the verticaldirection, forces caused by gravity alone are used. Accordingly, errorsin measurement of forces in the vertical direction do not cause errorsin joint moments.

[0042] Further, since the present invention does not need anacceleration of each portion of the leg except the acceleration ofgravity, noises are reduced and an operation speed is increased.Accordingly, robust and real-time operations can be easily achieved inobtaining moments acting around joints of the legs of the biped walkingsystem.

[0043] Further, in the invention in which information from the at leastone sensor is used to determine which leg or legs are in contact withthe ground, complicated processes for the determination are not requiredand therefore an operation speed is further increased. Accordingly,real-time operations can be still easily achieved in control of humanassist systems for assisting human operations and the like.

[0044] In the invention in which information from the at least onesensor set on the leg is used to determine which leg or legs are incontact with the ground, operations for the determination are notrequired and therefore real-time operations can be still easily achievedin control of human assist systems for assisting human operations andthe like. Further, the determination is made with reliability based onthe simple sensor.

[0045] A processor for moments acting around joints of a leg of a bipedwalking system, according to the present invention, is operable inassociation with angular sensors on the joints and at least one sensorset on the body of the biped walking system. The processor is configuredto perform the following steps. The steps include determining which legor legs are in contact with the ground, using information from the atleast one sensor set on the body and obtaining an attitude of the leg,using information from the angular sensors. The steps further includeobtaining a location of the center of gravity of the whole bodyincluding the leg, and obtaining the vertical component of a groundreaction force acting on the leg, based on which leg or legs are incontact with the ground. The steps further include obtaining a point ofapplication of the ground reaction force, using the attitude of the legand the location of the center of gravity of the whole body. The stepsfurther include obtaining the moments acting around the joints of theleg, using the vertical component of the ground reaction force acting onthe leg at the point of application of the ground reaction force, thevertical components of forces acting on the joints of the leg and a termof the acceleration of gravity and without using the horizontalcomponents of the forces acting on the joints of the leg and a term ofacceleration except the term of the acceleration of gravity.

[0046] A processor for moments acting around joints of a leg of a bipedwalking system, according to the present invention, is operable inassociation with angular sensors on the joints, at least one sensor seton the body of the biped walking system and at least one sensor set onthe leg. The processor is configured to perform the following steps. Thesteps include determining which leg or legs are in contact with theground, using information from the at least one sensor set on the legand obtaining an attitude of the leg, using information from the angularsensors. The steps further include obtaining a location of the center ofgravity of the whole body including the leg, and obtaining the verticalcomponent of a ground reaction force acting on the leg, based on whichleg or legs are in contact with the ground. The steps further includeobtaining a point of application of the ground reaction force, using theattitude of the leg and the location of the center of gravity of thewhole body. The steps further include obtaining the moments actingaround the joints of the leg, using the vertical component of the groundreaction force acting on the leg at the point of application of theground reaction force, the vertical components of forces acting on thejoints of the leg and a term of the acceleration of gravity and withoutusing the horizontal components of the forces acting on the joints ofthe leg and a term of acceleration except the term of the accelerationof gravity.

[0047] Thus, in the present invention, the vertical components alone offorces acting on the legs are used and the horizontal components are notused. Accordingly, errors in measurement of forces in the horizontaldirection, that is, accelerations in the horizontal direction do notcause errors in joint moments. Further, as forces in the verticaldirection, forces caused by gravity alone are used. Accordingly, errorsin measurement of forces in the vertical direction do not cause errorsin joint moments. Further, since the present invention does not need anacceleration of each portion of the leg except the acceleration ofgravity, noises are reduced and an operation speed is increased.Accordingly, robust and real-time operations can be easily achieved inobtaining moments acting around joints of the legs of the biped walkingsystem.

[0048] Further, in the invention in which information from the at leastone accelerometer is used to determine which leg or legs are in contactwith the ground, complicated processes for the determination are notrequired and therefore an operation speed is further increased.Accordingly, real-time operations can be still easily achieved incontrol of human assist systems for assisting human operations and thelike.

[0049] In the invention in which information from the at least onesensor set on the leg is used to determine which leg or legs are incontact with the ground, operations for the determination are notrequired and therefore real-time operations can be still easily achievedin control of human assist systems for assisting human operations andthe like. Further, the determination is made with reliability based onthe sensor.

DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 illustrates a basic idea of a method of estimating a groundreaction force, according to the present invention.

[0051]FIG. 2 shows in schematic form a person as a biped walking systemand devices equipped with the person.

[0052]FIG. 3 illustrates functions of a processor included in thedevices.

[0053]FIG. 4 shows a rigid body linked segment model used in operationsof the processor shown in FIG. 3.

[0054]FIG. 5 illustrates operations performed by a joint momentestimating module in the processor, shown in FIG. 3.

[0055]FIG. 6 shows a temporal change in an estimated value of momentacting on the hip joint while the person (1) is going up stairs,obtained thorough an embodiment of the present invention.

[0056]FIG. 7 shows a temporal change in an estimated value of momentacting on the knee joint while the person (1) is going up stairs,obtained thorough an embodiment of the present invention.

[0057]FIG. 8 shows a temporal change in an estimated value of momentacting on the hip joint while the person (1) is going down stairs,obtained thorough an embodiment of the present invention.

[0058]FIG. 9 shows a temporal change in an estimated value of momentacting on the knee joint while the person (1) is going down stairs,obtained thorough an embodiment of the present invention.

[0059]FIG. 10 shows a temporal change in an estimated value of momentacting on the hip joint while the person (1) is sitting in a chair,obtained thorough an embodiment of the present invention.

[0060]FIG. 11 shows a temporal change in an estimated value of momentacting on the knee joint while the person (1) is sitting in a chair,obtained thorough an embodiment of the present invention. FIG. 12 showsa temporal change in an estimated value of moment acting on the hipjoint while the person (1) is rising from a chair, obtained thorough anembodiment of the present invention.

[0061]FIG. 13 shows a temporal change in an estimated value of momentacting on the knee joint while the person (1) is rising from a chair,obtained thorough an embodiment of the present invention.

[0062]FIG. 14 is a flowchart showing operations of an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] One embodiment of the present invention will be describedreferring to FIGS. 1 to 5.

[0064] In this embodiment a method for obtaining torques to be appliedto joints and a method for estimating join moments, are applied to aperson as a biped walking system.

[0065] As illustrated in FIG. 2, a person (1) has a pair of legs (2, 2),a torso (5) comprising a hip (3) and a chest (4), a head (6) and a pairof arms (7, 7). In the torso (5) the hip (3) is connected with each ofthe legs (2, 2) through each of a pair of hip joints (8, 8) and issupported on the both legs (2, 2). The chest (4) is located over the hip(3) and can be declined toward the front of the person (1). The arms (7,7) extend from the lateral sides of the upper portion of the chest (4),over which the head (6) is supported.

[0066] Each of the legs (2, 2) has a thigh (9) extending from one of thehip joints (8) and a shin (11) extending from the end of the thigh via aknee joint (10). The end of the shin (11) is connected with a foot (13)via an ankle (ankle joint) (12).

[0067] In this embodiment the person (1) is equipped with devicesmentioned below in order to estimate a ground reaction force acting oneach (2) of the legs of the person (1) and moments acting on each (10)of the knee joints and each (8) of the hip joints.

[0068] The chest (4) of the torso (5) is equipped with a gyroscopicsensor (14) (hereinafter referred to as a chest gyroscopic sensor (14)),an accelerometer (15) (hereinafter referred to as a chest horizontalaccelerometer (15)), a processor (16) and a battery (17). The chestgyroscopic sensor (14) generates an output corresponding to an angularvelocity caused by inclination of the chest. The chest horizontalaccelerometer (15) generates an output corresponding to acceleration inthe horizontal direction at the chest (4). The processor (16) comprisesa CPU, a RAM, a ROM and other components. The battery (17) functions aspower source for the processor (16) and other devices. In this case, thechest gyroscopic sensor (14), the chest horizontal accelerometer (15),the processor (16) and the battery (17) are accommodated in a container(18) like a shoulder bag, fixed to the chest (4) with a belt or the likenot shown in the drawings and thus integrally fixed to the chest (4).

[0069] In more detail, output of the chest horizontal accelerometer (15)is acceleration in the anteroposterior direction in the horizontal crosssection of the chest (4) (orthogonal to the axis of the chest (4)). So,when the person (1) stands in an upright posture on the level ground,the acceleration is that in the horizontal direction (the direction ofthe x-axis of the absolute coordinate system shown in FIG. 2). However,when the chest (4) is inclined from the vertical direction (thedirection of the z-axis of the absolute coordinate system shown in FIG.2), the acceleration is that in the direction inclined by the angle bywhich the chest (4) is inclined from the vertical direction.

[0070] Further, the hip (3) of the torso (5) is equipped with agyroscopic sensor (19) (hereinafter referred to as a hip gyroscopicsensor (19)), an accelerometer (20) for generating an outputcorresponding to acceleration in the horizontal direction at the hip (3)(hereinafter referred to as a hip horizontal accelerometer (20)) andanother accelerometer (21) for generating an output corresponding toacceleration in the vertical direction at the hip (3) (hereinafterreferred to as a hip vertical accelerometer (21)). The hip gyroscopicsensor (19) generates an output corresponding to an angular velocitycaused by inclination of the hip. The above sensors are integrally fixedto the hip (3) with fixing means such as a belt or the like not shown inthe drawings.

[0071] In more detail, as in the case of the chest horizontalaccelerometer (15), the hip horizontal accelerometer (20) detectsacceleration in the anteroposterior direction in the horizontal crosssection of the hip (3) (orthogonal to the axis of the hip (3)). Further,in more detail, the hip vertical accelerometer (21) detects accelerationin the direction of the axis of the hip (3) (, which is orthogonal tothe direction of acceleration detected by the hip horizontalaccelerometer (20)). The hip horizontal accelerometer (20) and the hipvertical accelerometer (21) may be an integral biaxial accelerometer.

[0072] The hip joint (8) and knee joint (10) of each (2) of the legs areequipped respectively with a hip joint angular sensor (22) generating anoutput corresponding to a bending angle Δθc and a knee joint angularsensor (23) generating an output corresponding to a bending angle Δθd.Although FIG. 2 shows the hip joint angular sensor (22) concerning thehip joint (8) of the leg (2) on the right side of the person (1), alone,the hip joint (8) of the leg (2) on the left side of the person (1) isequipped with another hip joint angular sensor (22) just as in the caseof the right side.

[0073] The angular sensors (22, 23) comprise potentiometers, forexample, and are attached to each (2) of the legs by such means as aband not shown in the drawing. In more detail, a bending angle Δθcdetected by each (22) of the hip joint angular sensors is a rotationangle around the hip joint (8) (around the lateral axis of the hip joint(8)) of the thigh (9) of each of the legs with respect to the hip (3).The reference angle is the rotation angle measured when the hip (3) isin proper relation with each (2) of the legs. For example, the referenceangle is the rotation angle measured when the axis of the hip (3) andthe axis of the thigh (9) are substantially parallel to each other as inthe case that the person (1) is in an upright posture. Similarly, abending angle Δθd detected by each (23) of the knee joint angularsensors is a rotation angle around the knee joint (10) (around thelateral axis of the hip knee joint (10)) of the shin (11) of each of thelegs with respect to the thigh (9). The reference angle is the rotationangle measured when the thigh (9) is in proper relation with the shin(11). For example, the reference angle is the rotation angle measuredwhen the axis of the thigh (9) and the axis of the shin (11) aresubstantially parallel to each other.

[0074] One or more foot switches (24) may be provided with portions ofthe legs, to be in contact with the ground. Foot switches (24) detectwhich leg or legs are in contact with the ground, with a contact method.

[0075] Alternatively, range sensors with an infrared method or the like,not shown in the drawings may be attached to the ankle joints or theknee joints. In this case, distances to the floor have been previouslymeasured in an upright posture. Based on the previously measureddistances and distances measured by the sensors in walking, it isdetermined which leg or legs are in contact with the ground.

[0076] The sensors (14, 15 and 19 to 24) and the range sensors not shownin the drawings, are connected with the processor (16) via signal linesnot shown in the drawings to deliver their outputs to the processor(16).

[0077] The processor (16) is provided with functional modules as shownin FIG. 3. The processor (16) may be provided with a leg-motiondetermining module (25). The leg-motion determining module (25)determines whether the legs (2, 2) of the person (1) are in asingle-support phase (as shown in FIG. 1(a)) or in a double-supportphase (as shown in FIG. 1(b)), using data detected by the hip verticalaccelerometer (21) and predetermined thresholds. Alternatively, footswitches (24) on portions to be in contact with the ground or rangesensors not shown in the drawings, may be provided so that informationfrom the foot switches (24) or the range sensors can be used todetermine which leg or legs are in contact with the ground. Further, theprocessor (16) is provided with a chest inclining angle-measuring module(26) and a hip inclining angle-measuring module (27). The chestinclining angle-measuring module (26) measures an inclining angle θa ofthe chest (4) (more specifically, for example, an inclining angle θafrom the vertical direction as shown in FIG. 2) in the absolutecoordinate system Cf, using data detected by the chest horizontalaccelerometer (15) and chest gyroscopic sensor (14). The hip incliningangle-measuring module (27) measures an inclining angle θb of the hip(3) (more specifically, for example, an inclining angle θb from thevertical direction as shown in FIG. 2) in the absolute coordinate systemCf, using data detected by the hip horizontal accelerometer (20) and hipgyroscopic sensor (19).

[0078] Further, the processor (16) is provided with areference-acceleration measuring module (28). The reference accelerationmeasuring module (28) obtains the vertical component a_(o)z of(translational) acceleration of the origin point O in the bodycoordinate system Cp (xz coordinates in FIG. 2), using data detected bythe hip horizontal accelerometer (20) and the hip vertical accelerometer(21) and an inclining angle θb of the hip (3) detected by the hipinclining angle-measuring module (27). The body coordinate system Cp (xzcoordinates in FIG. 2) is fixed to the hip (3) as the reference point ofthe person (1) in this embodiment, as shown in FIG. 2. In more detail,the body coordinate system Cp has its origin point O at the middle pointof the line segment connecting the centers of the right and left hipjoints (8, 8) of the person (1), its z axis in the vertical directionand its x axis in the moving direction of the person (1) in thehorizontal plane. The directions of the three axes of the bodycoordinate system Cp are identical with those of the absolute coordinatesystem Cf.

[0079] The processor (16) is provided with a leg-attitude computingmodule (32). The module (32) obtains an inclining angle θc of the thigh(9) of each (2) of the legs and an inclining angle θd of the shin (11)of each (2) of the legs in the absolute coordinate system Cf. Morespecifically, for example, the inclining angles are those from thevertical direction, as shown in FIG. 2. The module (32) obtains theinclining angles, using data detected by the hip joint angular sensor(22) and knee joint angular sensor (23) of each of the legs and aninclining angle θb of the hip (3) measure by the hip incliningangle-measuring module (27).

[0080] The processor (16) is provided with a portion center ofgravity-location computing module (31). The module (31) obtainslocations of the centers of gravity of portions of the person (1)corresponding to rigid segments of a rigid body linked segment modelmentioned below (in more detail which leg or legs, locations of thecenters of gravity of portions corresponding to rigid segments, in thebody coordinate system Cp mentioned above). The module (31) obtains thelocations of the centers of gravity, using an inclining angle θa of thechest (4) measured by the chest inclining angle-measuring module (26),an inclining angle θb of the hip (3) measured by the hip incliningangle-measuring module (27) and an inclining angle θc of the thigh (9)of each (2) of the legs and an inclining angle θd of the shin (11) ofeach (2) of the legs, obtained by the leg-attitude computing module(32).

[0081] The portion center of gravity-location computing module (31) andleg-attitude computing module (32) constitute a body geometric model(30).

[0082] Further, the processor (16) is provided with a body center ofgravity location computing module (41) and a body center ofgravity-acceleration computing module (42). The module (41) obtains thecenter of gravity of the whole person (1) in the body coordinate systemCp, using locations of the centers of gravity of portions correspondingto rigid segments. The center of gravity-acceleration computing module(42) obtains vertical component az of acceleration of the body center ofgravity G0 in the body coordinate system Cp (shown in FIG. 1).

[0083] The body center of gravity location computing module (41) andcenter of gravity-acceleration computing module (42) constitute a bodymass distribution model (40).

[0084] The processor (16) is provided with a module (50) for estimatinga point of application of ground reaction force. The module (50) locatesa point of application of ground reaction force acting on a leg incontact with the ground. The module (50) locates the point, using aninclining angle θc of the thigh (9) and an inclining angle θd of theshin (11) obtained by the leg-attitude computing module (32) and thecenter of gravity of the whole obtained by the body center of gravitylocation computing module (41). Alternatively, information from footswitches (24) or range sensors not shown in the drawings can be used toestimate a point of application of ground reaction force, as mentionedin more detail below.

[0085] The processor (16) is provided with a ground reaction-forceestimating module (60) for obtaining a ground reaction force acting oneach (2) of the legs. The ground reaction-force estimating module (60)obtains a location of the ankle (12) of each (2) of the legs, as aspecific part of each (2) of the legs, with respect to the center ofgravity of the whole body G0 (hereinafter referred to as body center ofgravity G0). In more detail, the location is represented by (ΔX f, ΔZ f)or (ΔX r, ΔZ r) in Equation (5). The module (60) obtains the location,using a location of the body center of gravity G0, obtained by the bodycenter of gravity location computing module (41) and inclining angles θcof the thigh (9) and θd of the shin (11) of each (2) of the legs,obtained by the leg-attitude computing module (32). Further, the module(60) obtains an estimated value of the vertical component of the groundreaction force acting on each (2) of the legs, using the location, thevertical component az of acceleration of the body center of gravity andstate of which leg or legs are in contact with the ground, determined bythe leg-motion determining module (25). The vertical component az isobtained by the center of gravity-acceleration computing module (42).

[0086] The processor (16) is provided with a joint moment estimatingmodule (71) for estimating moments acting on the knee joint (10) and thehip joint (8) of each of the legs. The module (71) estimates moments,using a value estimated by the ground reaction-force estimating module(60), a location estimated by the module (50) for estimating a point ofapplication of ground reaction force and inclining angles θc and θd ofthe thigh (9) and the shin (11) of each (2) of the legs, obtained by theleg-attitude computing module (32).

[0087] The processor (16) is provided with a gravity compensationtorque-computing module (72) for obtaining assist torque for assistingthe person, that is, gravity compensation torques by multiplyingestimated values of moments obtained by the joint moment estimatingmodule (71), by certain factors.

[0088] The joint moment estimating module (71) and gravity compensationtorque-computing module (72) constitute a gravity compensation model(70).

[0089] Operations of this embodiment carried out by the modules of theprocessor (16) will be described in detail below.

[0090] In this embodiment the processor (16) starts to carry out thefollowing successive operations periodically to obtain an estimatedvalue of the ground reaction force acting on each (2) of the legs or thelike, when the person (1) with his or her legs (2, 2) being in contactwith the ground, turns on the power switch of the processor (16) notshown in the drawings, before he or she starts moving his or her legs,for example walking.

[0091] First, the processor (16) has the leg-motion determining module(25) carry out processes. In the processes of the leg-motion determiningmodule (25), an acceleration value at the hip (3) in the upward andvertical direction, detected by the hip vertical accelerometer (21), iscompared with a predetermined threshold periodically. When the detectedacceleration value exceeds the threshold, it is determined that themotion is in a single-support phase in which the front leg is in contactwith the ground as shown in FIG. 1(a). When the detected accelerationvalue is less than or equal to the threshold, it is determined that themotion is in a double-support phase as shown in FIG. 1(b).

[0092] Alternatively, outputs of the foot switches (24) provided onportions of the legs to be in contact with the ground or the rangesensors not shown in the drawings, are read periodically to determinewhich leg or legs are in contact with the ground.

[0093] Concurrently with the above-mentioned processes of the footswitches (24) or the range sensors, or of the leg-motion determiningmodule (25), the processor (16) carries out processes of the chestinclining angle-measuring module (26) and hip inclining angle-measuringmodule (27). In the processes of the chest inclining angle-measuringmodule (26), an inclining angle θa of the chest (4) in the absolutecoordinate system Cf is successively obtained by processing data ofacceleration in the horizontal direction detected by the chesthorizontal accelerometer (15) and data of angular velocity detected bythe chest gyroscopic sensor (14), with a known method using Karmanfilter. Similarly, in the processes of the hip inclining angle-measuringmodule (27), an inclining angle θb of the hip (3) in the absolutecoordinate system Cf is successively obtained by processing data ofacceleration in the horizontal direction detected by the hip horizontalaccelerometer (20) and data of angular velocity detected by the hipgyroscopic sensor (19), with a known method using Karman filter. In thisembodiment, for example, an inclining angle θa of the chest (4) and aninclining angle θb of the hip (3) in the absolute coordinate system Cf,are those from the vertical direction (the direction of gravity).

[0094] An inclining angle of the chest (4) and an inclining angle of thehip (3) can also be obtained by integrating data of angular velocitiesdetected by gyroscopic sensors (14) and (19), for example. However, themethod using Karman filter in this embodiment enables more accuratemeasurements of an inclining angle θa of the chest (4) and an incliningangle θb of the hip (3).

[0095] Next the processor (16) carries out processes of the leg-attitudecomputing module (32) and reference-acceleration measuring module (28).

[0096] In the processes of the leg-attitude computing module (32), aninclining angle θc of the thigh (9) of each (2) of the legs and aninclining angle θd of the shin (11) of each (2) of the legs in theabsolute coordinate system Cf, are periodically obtained as below.Inclining angles are those from the vertical direction as shown in FIG.2. An inclining angle θc of the thigh (9) of each (2) of the legs, isobtained by substituting a current value of bending angle Δθc of the hipjoint (8) detected by the hip joint angular sensor (22) and a currentvalue of inclining angle θb of the hip (3), obtained by the hipinclining angle-measuring module (27), into the following equation.

θc=θb+Δθc  (5)

[0097] A value of inclining angle θb of the hip (3) becomes negativewhen the hip (3) is inclined from the vertical direction in such away asthe top end of the hip (3) is located forward than the bottom end,toward the front of the person (1). A value of bending angle Δθc becomespositive when the thigh (9) is inclined in such away as the bottom endof the thigh (9) is located toward the front of the person (1).

[0098] An inclining angle θd of the shin (11) of each (2) of the legs isobtained by substituting a current value of inclining angle θc of thethigh (9) previously obtained as mentioned above and a current value ofbending angle Δθd detected by knee joint angular sensor (23) attached tothe leg, into the following equation.

θd=θc−Δθd  (6)

[0099] A value of bending angle at the knee joint (10) becomes positivewhen the shin (11) is inclined from the axis of the thigh (9) toward theback.

[0100] Next the processor (16) carries out processes of the portioncenter of gravity-location computing module (31) to obtain locations ofthe centers of gravity in the body coordinate system Cp, of portions ofthe person (1) corresponding to rigid segments, using a rigid bodylinked segment model mentioned below.

[0101] As shown in FIG. 4, a rigid body linked segment model R used inthis embodiment represents the person (1) as a combination of rigidbodies (R1, R1) corresponding to the thighs (9, 9) of the legs, rigidbodies (R2, R2) corresponding to the shins (11, 11) of the legs, a rigidbody R3 corresponding to the hip (3) and a rigid body R4 correspondingto a portion (38) comprising the chest (4), the arms (7, 7) and the head(6). The portion is hereinafter referred to as the upper part (38). Acoupler between R1 and R3 and that between R1 and R2 correspondrespectively to one (8) of the hip joints and one (10) of the kneejoints. By a portion corresponding to a coupler between R3 and R4, thehip (3) supports the chest (4) inclinably.

[0102] In this embodiment locations of the centers of gravity G1, G2, G3and G4 of the portions (the thighs (9, 9) and the shins (11, 11) of thelegs, the hip (3) and the upper part (38)) corresponding to rigidsegments R1 to R4 in the rigid body linked segment model R, arepreviously obtained and stored in a memory connected to the processor(16), not shown in the drawings.

[0103] Locations of the centers of gravity G1, G2, G3 and G4 of theportions, stored in the processor (16), are those in a coordinate systemfixed to each of the portions. In this case, a distance from the centerof the joint at an end of a portion measured in the axial direction, isused to represent each of the locations of the centers of gravity G1,G2, G3 and G4 of the portions. For example, as shown in FIG. 4, alocation of the center of gravity of one (9) of the thigh is representedby a distance t1 from the center of the hip joint (8) of the thigh (9)in the axial direction of the thigh (9). A location of the center ofgravity of one (11) of the shin is represented by a distance t2 from thecenter of the knee joint (10) of the shin (11) in the axial direction ofthe shin (11). Values of distance t1 and distance t2 are previouslystored in the processor (16). Locations of the centers of gravity G3 andG4 of the other portions are represented similarly.

[0104] Strictly speaking, motions of the arms (7, 7) affect a locationof the center of gravity G4 of the upper part (38). However, in walkinglocations of the arms (7, 7) are generally symmetric with respect to theaxis of the chest (4) and therefore a location of the center of gravityG4 of the upper part (38) does not change significantly, remainingsubstantially identical with that in an upright posture, for example.

[0105] Further, in this embodiment, other data of the portions (thethighs (9, 9) and the shins (11, 11) of the legs, the hip (3) and theupper part (38)), including weights and sizes (for example, lengths)besides locations of the centers of gravity G1, G2, G3 and G4, arepreviously obtained and stored in the processor (16).

[0106] A weight of one (11) of the shins includes that of correspondingone (13) of the feet. Data stored previously in the processor (16) maybe obtained through actual measurements, or may be estimated through aheight and a weight of the person (1) based on average values obtainedfrom statistical data of persons. Generally, locations of the centers ofgravity G1, G2, G3 and G4, weights and sizes of the portions show acorrelation with heights and weights of persons. Accordingly, locationsof the centers of gravity G1, G2, G3 and G4, weights and sizes of theportions can be estimated based on data of a height and a weight of aperson with a relatively high accuracy.

[0107] The portion center of gravity-location computing module (31)obtains locations of the centers of gravity G1, G2, G3 and G4 of theportions corresponding to rigid segments in the body coordinate systemCp (xz coordinates in FIG. 2) fixed to the hip (3) and having the originpoint O, from the following data. The data include those previouslystored in the processor (16) as mentioned above, current values of aninclining angle θa of the chest (4) and an inclining angle θb of the hip(3) and current values of an inclining angle θc of the thigh (9) of each(2) of the legs and an inclining angle θd of the shin (11) of each (2)of the legs. An inclining angle θa of the chest (4) (an inclining angleof the upper part (38)) and an inclining angle θb of the hip (3) areobtained respectively by the chest inclining angle-measuring module (26)and hip inclining angle-measuring module (27). An inclining angle θc ofthe thigh (9) and an inclining angle θd of the shin (11) are obtained bythe leg-attitude computing module (32).

[0108] Since inclining angles θa to θd of each of the portionscorresponding to rigid segments (the thigh (9) and the shin (11) of each(2) of the legs, the hip (3), and the upper part (38)) are obtained asmentioned above, locations and attitudes of the portions correspondingto rigid segments can be determined in the body coordinate system Cp.Accordingly, locations of the centers of gravity G1, G2, G3 and G4 ofthe portions corresponding to rigid segments can be obtained.

[0109] More specifically, for example, in FIG. 4 an inclining angle(from the z axis direction) of the thigh (9) of the leg (2) on the leftside is θc. In FIG. 4, θc is less than zero. Accordingly, coordinates ofthe location of the center of gravity G1 of the thigh (9) in the bodycoordinate system Cp are (t1·sin θc, −t1·cos θc). Further, an incliningangle of the shin (11) of the leg (2) on the left side is θd. In FIG. 4,θd is less than zero. Accordingly, provided that a length of the thigh(9) is Lc, coordinates of the location of the center of gravity G2 ofthe shin (11) in the body coordinate system Cp are (L c·sin θc+t2·sinθd, −L c·cos θc−t2·cos θd). Locations of the centers of gravity of thethigh (9) and the shin (11) of the other leg (2), the hip (3) and theupper part (38) can be obtained in a similar way as mentioned above.

[0110] After the portion center of gravity-location computing module(31) has obtained locations of the centers of gravity G1, G2, G3 and G4of the portions corresponding to rigid segments in the body coordinatesystem Cp, the processor (16) carries out operations of the body centerof gravity location computing module (41). The body center of gravitylocation computing module (41) obtains a location (xg, zg) of the bodycenter of gravity G0 of the person (1), using location data of G1, G2,G3 and G4 and weight data of the portions corresponding to rigidsegments.

[0111] In the body coordinate system Cp, a location of the center ofgravity G3 and a weight of the hip (3) are represented respectively by(x3, z3) and m3. A location of the center of gravity G4 and a weight ofthe upper part (38) are represented respectively by (x4, z4) and m4. Alocation of the center of gravity G1 and a weight of the thigh (9) ofthe leg (2) on the left side of the person (1) are representedrespectively by (x1L, z1L) and m1L. A location of the center of gravityG2 and a weight of the shin (11) of the leg (2) on the left side of theperson (1) are represented respectively by (x2L, z2L) and m2L. Alocation of the center of gravity G1 and a weight of the thigh (9) ofthe leg (2) on the right side of the person (1) are representedrespectively by (x1R, z1R) and m1R. A location of the center of gravityG2 and a weight of the shin (11) of the leg (2) on the rioght side ofthe person (1) are represented respectively by (x2 R, z2 R) and m2R. Aweight of the person (1) is represented by M (=m1L+m2L+m1R+m2R+m3+m4).Then, a location of the body center of gravity G0 of the person (1) isobtained by the following equation (7). $\begin{matrix}\begin{matrix}\begin{matrix}{{x\quad g} = ( {{{m1L} \cdot {x1L}} + {{m1R} \cdot {x1R}} + {2m\quad {L \cdot {x2L}}} + {{m2R} \cdot}} } \\{ {{x2R} + {{m3} \cdot {x3}} + {{m4} \cdot {x4}}} )/M}\end{matrix} \\\begin{matrix}{{z\quad g} = ( {{{m1L} \cdot {z1L}} + {{m1R} \cdot {z1R}} + {{m2}\quad {L \cdot {z2L}}} + {{m2R} \cdot}} } \\{ {{z2R} + {{m3} \cdot {z3}} + {{m4} \cdot {z4}}} )/M}\end{matrix}\end{matrix} & (7)\end{matrix}$

[0112] Then the processor (16) carries out operations of the groundreaction-force estimating module (60) as below.

[0113] When it is determined during a current period through theleg-motion determining module (25), foot switches (24) or range sensorsnot shown in the drawings that motion of the legs are in asingle-support phase, an estimated value of the vertical component Fz ofthe ground reaction force acting on the leg (2) in contact with theground, is obtained using Equation (2).

[0114] In the above case, the vertical component Fz of the groundreaction force acting on the leg (2) not in contact with the ground (theleg without load), is zero.

[0115] When it is determined during a current period through theleg-motion determining module (25), foot switches (24) or range sensorsnot shown in the drawings that motion of the legs are in adouble-support phase, estimated values of the vertical components Ffzand Frz of the ground reaction forces acting on each (2) of the legs,are obtained using Equation (4).

[0116] The processor (16) carries out operations of the module (50) forestimating a point of application of ground reaction force concurrentlywith the above operations of the body center of gravity locationcomputing module (41) and the ground reaction-force estimating module(60).

[0117] In operations of the module (50) for estimating a point ofapplication of ground reaction force, a vector from the ankle (12) ofeach (2) of the legs to the point of application of the ground reactionforce on the foot (13) of the leg, is obtained in the procedure below.The point of application of the ground reaction force is the point onwhich the whole ground reaction force acting on the portion of the foot(13), in contact with the ground, can be considered to be concentrated.The above vector is a location vector of the point of application of theground reaction force, with respect to the ankle (12) and is hereinafterreferred to as a vector of a point of application of the ground reactionforce.

[0118] As shown in FIG. 2, the ankle joint at the ankle 12 isrepresented as 12A while the joint at the front end of the foot (13)(the so-called MP joint) is represented as 12B. First, the horizontalcomponent x12 of coordinates of a location of the ankle joint (12A) isobtained. More specifically, in FIG. 4, provided that a length of theshin (11) (a length from the center of the knee joint (10) to the ankle(12)) of the leg on the left side of the drawing is Ld, coordinates (x12, z 12) of location of the ankle (12) in the body coordinate system Cpare (L c·sin θc+L d·sin θd, −L c·cos θc−L d·cos θd). In FIG. 4, θc andθd are less than zero. Data on the other leg can be obtained similarly.Further, provided that a horizontal distance between the ankle joint(12A) and the MP joint (12B) is a constant D, the horizontal componentx12B of coordinates of a location of the MP joint (12B) is obtainedthrough the following equation.

X 12 B=x 12+D

[0119] Then walking mode is determined. If the vertical component of adifference between a location of the left ankle joint and that of theright ankle joint, as obtained in such a way as mentioned above, exceedsa certain threshold while the both legs are in contact with the ground,it is determined that the person (1) is going up or down stairs or goinguphill or downhill. Otherwise, it is determined that the person (1) iswalking under normal conditions.

[0120] Then when the person (1) is walking under normal conditions, thehorizontal component of the endpoint of the vector of a point ofapplication of the ground reaction force, is obtained by comparing thehorizontal components obtained as mentioned above, in the followingprocedure. If the horizontal component xg of G0 is less than thehorizontal component x12 of the ankle joint 12A, the horizontalcomponent of the endpoint of the vector of a point of application of theground reaction force is assumed to be the horizontal component x12 ofthe ankle joint 12A. If the horizontal component xg of G0 is betweenhorizontal component x12 of the ankle joint 12A and the horizontalcomponent x12B of the MP joint 12B, the horizontal component of theendpoint of the vector of a point of application of the ground reactionforce is assumed to be the horizontal component xg of G0. If thehorizontal component xg of G0 is greater than the horizontal componentx12B of the MP joint 12B, the horizontal component of the endpoint ofthe vector of a point of application of the ground reaction force isassumed to be the horizontal component x12B of the MP joint 12B.

[0121] When the person (1) is going up or down stairs or going uphill ordownhill, the horizontal component of the endpoint of the vector of apoint of application of the ground reaction force is always assumed tobe the horizontal component x12B of the MP joint (12B).

[0122] The vertical component of the vector of a point of application ofthe ground reaction force, is obtained with the assumption that adistance between the ankle joint 12A and the ground is a constant E.

[0123] In the above procedure, the vector of a point of application ofthe ground reaction force, can be obtained. The vector is starting atthe ankle joint 12A and ending at the point of application of the groundreaction force.

[0124] Alternatively the module (50) for estimating a point ofapplication of ground reaction force, can obtain the vector of a pointof application of the ground reaction force, using information from thefoot switches (24) or range sensors in the following procedure. In thiscase, the contact-type foot switches (24) or the range sensors for theankle joints (12A) and the MP joints (12B) are used to determine whetheror not each of the heels and each of tiptoes are in contact with theground. If both foot switches (24) or both range sensors for the anklejoint (12A) and the MP joint (12B) indicate that the portions are incontact with the ground, the horizontal component of the vector of apoint of application of the ground reaction force, is obtained in asimilar procedure to that in the above case where the person (1) iswalking under normal conditions. If the foot switch (24) or range sensorfor the ankle joint (12A), alone indicates that the portion is incontact with the ground, the horizontal component of the endpoint of thevector of a point of application of the ground reaction force is assumedto be the horizontal component x12 of the location coordinates of theankle joint (12A). If the foot switch (24) or range sensor for the MPjoint (12B), alone indicates that the portion is in contact with theground, the horizontal component of the endpoint of the vector of apoint of application of the ground reaction force is assumed to be thehorizontal component x12B of the location coordinates of the MP joint(12B).

[0125] The vertical component of the vector of a point of application ofthe ground reaction force, is obtained with the assumption that adistance between the ankle joint (12A) and the ground is a constant E.

[0126] In the above procedure, the vector of a point of application ofthe ground reaction force, can be obtained, using information from thefoot switches (24) or range sensors. The vector is starting at the anklejoint 12A and ending at the point of application of the ground reactionforce.

[0127] After having estimated the location of a point of application ofthe ground reaction force, the processor (16) caries out operations ofthe joint moment estimating module (71) to obtain moments acting on theknee joint (10) and the hip joint (8) of each (2) of the legs. Theoperations are carried out based on the so-called inverse dynamicsmodel, using current values of data obtained by the groundreaction-force estimating module (60), module (50) for estimating apoint of application of ground reaction force and leg-attitude computingmodule (32). The inverse dynamics model uses equations of translationalmotion and rotational motion for each portion of the person (1),corresponding to rigid segment, to obtain moments acting on the jointsof each of the legs, one after another, from moment acting on the jointnext to the point of application of ground reaction force. In thisembodiment, moment acting on the knee joint (10) of each of the legs, isobtained and then that acting on the hip joint (8) is obtained.

[0128] In more detail, referring to FIG. 5, a force acting on the ankle(12) at an end of the shin (11) of each (2) of the legs (a jointreaction force), a force acting on the knee joint (10) of the shin (11)(a joint reaction force) and an translational acceleration of the centerof gravity G2 of the shin (11) are represented by components in theabsolute coordinate system Cf as below. The representations are^(T)(F₁x, F₁z), ^(T)(F₂x, F₂z) and ^(T)(a_(2x), a_(2z)). A weight of theshin (11) is represented as m₂. If acceleration terms except the term ofthe acceleration of gravity are neglected, the equation of translationalmotion of the center of gravity G2 of the shin (11) is as below.

^(T)(0, 0)=^(T)(F ₁ x−F ₂ x, F ₁ z−F ₂ z−m ₂ ·g)

[0129] Accordingly, as to the vertical components, the equation ofmotion is as below.

F ₂ z=F ₁ z−m ₂ ·g  (8)

[0130] An approximate value of the vertical component F₁z of the jointreaction force acting on the ankle (12) at an end of the shin (11) isequal to an estimated value of the vertical component of the groundreaction force obtained by the ground reaction-force estimating module(60) for the shin (11) of the leg (2). In more detail, in asingle-support phase the vertical component F₁z of the joint reactionforce is the vertical component Fz=M·g of the ground reaction forceobtained through Equation (2) when the leg is in contact with theground. The vertical component F₁z is zero when the leg is idle.Further, in a double-support phase the vertical component F₁z of thejoint reaction force is the vertical component Frz=(½)·M·g of the groundreaction force in Equation (4) when the leg is the rear one of theperson (1) in the traveling direction. The vertical component F₁z of thejoint reaction force is the vertical component Ffz=(½)·M·g of the groundreaction force in Equation (5) when the leg is the front one of theperson (1) in the traveling direction.

[0131] Accordingly, the vertical component F₂z of the joint reactionforce acting on the knee joint (10) of each of the legs, can be obtainedby substituting data of the vertical component F₁z of the groundreaction force obtained by the ground reaction-force estimating module(60), data of a weight m₂ of the shin (11), previously obtained and avalue of the acceleration of gravity g, into Equation (8).

[0132] Referring to FIG. 5, a moment acting on the ankle (12) at an endof the shin (11) of each (2) of the legs, a moment acting on the hipjoint (10) of the shin (11), a moment of inertia around the center ofgravity G2 of the shin (11) and an angular acceleration around thecenter of gravity G2 of the shin (11), are represented as M₁, M₂,I_(G 2) and α₂. Referring to FIG. 4, a distance between the center ofgravity G2 of the shin (11) and the knee joint (10) and a distancebetween the center of gravity G2 of the shin (11) and the ankle (12) arerepresented respectively as t₂ and t₂′ (=Ld−t₂). If horizontal forceterms and angular acceleration terms are removed, the equation ofrotational motion around the center of gravity G2 of the shin (11) is asbelow.

I _(G2)·α₂=0=M ₁ −M ₂ −F ₁ z·t ₂′·sin θd−F ₂ z·t ₂·sin θd

[0133] The equation can be rewritten as below.

M ₂ =M ₁ −F ₁ z·t ₂′·sin θd−F ₂ z·t ₂·sin θd  (9)

[0134] M₁ in Equation (11) is a moment obtained as an outer (vector)product of a vector of a point of application of ground reaction force,obtained by the module (50) for estimating a point of application ofground reaction force and a vector of ground reaction force, obtained bythe ground reaction-force estimating module (60). Further, since angularacceleration terms are removed, α₂ is assumed to be zero. θd is aninclining angle of the shin (11), obtained by the leg-attitude computingmodule (32). F₁z is an estimated value of the vertical component of aground reaction force, obtained by the ground reaction-force estimatingmodule (60), as mentioned above. F₂z is obtained through Equation (10).

[0135] Accordingly, moment M₂ acting on the knee joint (10) is obtainedby substituting the following data into Equation (11). The data includesan estimated value of the vertical component of a ground reaction force,obtained by the ground reaction-force estimating module (60) and avector of a point of application of ground reaction force, obtained bythe module (50) for estimating a point of application of ground reactionforce an inclining angle of the shin (11). The data further includes aninclining angle θd of the shin (11), obtained by the leg-attitudecomputing module (32), the vertical component F₂z of a joint reactionforce, obtained through Equation (10), a size (d) of the shin (11) and alocation (t₂) of the center of gravity G2.

[0136] The joint moment estimating module (71) obtains moment M₂ actingon the knee joint (10) of the shin (11) as mentioned above. Then themodule obtains a moment acting on the hip joint (8) of the thigh (9) ina way similar to that mentioned above. The basic idea of the operationis identical with that for obtaining moment M₂ acting on the knee joint(10) and therefore detailed explanation with a drawing is not given. Theoutline of the operation is as below.

[0137] First, the vertical component F₃z of the joint reaction forceacting on the knee joint (8) of the thigh (9) is obtained throughEquation (10) (which has the form identical with that of Equation (8))on translational motion of the center of gravity G1 (FIG. 4) of thethigh (9).

F ₃ z=F ₂ z−m ₁ ·g  (10)

[0138] F₂z is the vertical component of the joint reaction force on theknee joint (10), previously obtained through Equation (8). m₁ is aweight of the thigh (9) previously obtained and g is the acceleration ofgravity.

[0139] Then, moment M₃ acting on the hip joint (8) of the thigh (9) isobtained through Equation (11) (which has the form identical with thatof Equation (9)) on rotational motion of the center of gravity G1 of thethigh (9).

M ₃ =M ₂ −F ₂ z·t ₁′·sin θc−F ₃ z·t ₁·sin θc  (11)

[0140] M₂ is a moment on the knee joint (10), obtained through Equation(9). F₂z is the vertical component of the joint reaction force on theknee joint (10), obtained through Equation (10). F₃z is the verticalcomponent of the joint reaction force on the hip joint (8), obtainedthrough Equation (12). θc is an inclining angle of the thigh (9)obtained by the leg-attitude computing module (32). t₁ is a distancefrom the center of the hip joint (8) to the center of gravity G1 of thethigh (9), as shown in FIG. 4, while t₁′ is a distance from the centerof the knee joint (10) to the center of gravity G1 of the thigh (9), asshown as L c−t₁ in FIG. 4. These values t₁ and t₁′ are determined basedon a location of the center of gravity G1 and a size (length) of thethigh (9), previously obtained.

[0141] Then, a gravity compensation torque computing module (72)computes a gravity compensation torques by multiplying values of kneejoint moments and hip joint moments, obtained by the joint momentestimating module (71), by certain factors. The factors are given asconstants refereed to as assist ratios. In human assist systemscomprising electric motors or the like for supplying knee joints (10)and hip joints (8) with assist torques, to assist operations of theperson (1), assist ratios are determine to compensate certain ratios ofjoint moments. Gravity compensation torques obtained as mentioned above,are used for control of human assist systems.

[0142] The operations mentioned above are successively carried outperiodically to successively estimate, in real time, ground reactionforce acting on each (2) of the legs, moments acting on the knee joint(10) and hip joint (8) of each (2) of the legs and gravity compensationtorques on the knee joint (10) and hip joint (8).

[0143] The above-mentioned operations of an embodiment of the presentinvention are summarized in FIG. 14. At step S1410 the leg-motiondetermining module (25) determines which leg or legs are in contact withthe ground. In place of the leg-motion determining module (25), footswitches (24) or range sensors may be used for the determination. Atstep S1420, the leg-attitude computing module (32) obtains attitudes ofthe legs. At step S1430, the body center of gravity-location computingmodule (41) obtains the center of gravity of the body. At step S1440,the center of gravity-acceleration computing module (42) obtains anacceleration of the body center of gravity. At step S1450, the groundreaction-force estimating module (60) obtains the vertical component ofa ground reaction force. At step S1460, the module (50) for estimating apoint of application of ground reaction force, obtains a point ofapplication of ground reaction force. At step S1470, the joint momentestimating module (71) obtains moments acting on the joints. At stepS1480, gravity compensation torque-computing module (72) obtains torqueto be applied to the joints.

[0144] Temporal changes in estimated values of moments acting on thejoints, obtained by the above-mentioned operations of the processor(16), are shown with Δ in FIGS. 6 to 13. In FIGS. 6 to 13, ⋄ showsestimated values of moments acting on the joints, obtained through stepsin which operations are performed using terms of accelerations and termsof horizontal forces, with subsequent filtering. In FIGS. 6 to 13, □shows estimated values of moments acting on the joints, obtained throughsteps in which operations include terms of accelerations and terms ofhorizontal forces, without subsequent filtering. FIG. 6 shows momentsacting on the hip joint while the person (1) is going up stairs. FIG. 7shows moments acting on the knee joint while the person (1) is going upstairs. FIG. 8 shows moments acting on the hip joint while the person(1) is going down stairs. FIG. 9 shows moments acting on the knee jointwhile the person (1) is going down stairs. FIG. 10 shows moments actingon the hip joint while the person (1) is sitting in a chair. FIG. 11shows moments acting on the knee joint while the person (1) is sittingin a chair. FIG. 12 shows moments acting on the hip joint while theperson (1) is rising from a chair. FIG. 13 shows moments acting on theknee joint while the person (1) is rising from a chair.

[0145] In the steps of the present invention for obtaining momentsacting on the joints, operations are performed without using terms ofaccelerations and terms of horizontal forces. However, referring toFIGS. 6 to 13, changes in estimated values of moments on the jointsaccording to the present invention, are similar to those obtainedthrough a method in which operations are performed using terms ofaccelerations and terms of horizontal forces. In particular, changes inestimated values during periods while the person (1) is sitting in achair and the person (1) is rising from a chair, are very similar tothose obtained through a method in which operations are performed usingterms of accelerations and terms of horizontal forces.

[0146] As mentioned above, the embodiment allows real-time and easyestimation of ground reaction force acting on each (2) of the legs andmoments acting on the hip joint (8) and the knee joint (10) of each (2)of the legs, using relatively small and light sensors and withoutsetting to the legs (2) such sensors as hinder the person (1) fromwalking or make load of motion heavy. The relatively small and lightsensors include the angular sensors (22, 23) set on the hip joints (8)and the knee joints (10) and the gyroscopic sensors (14, 19) andaccelerometers (15, 20, 21). Further, in the steps for obtaining momentsacting on the joints, operations are performed without using terms ofaccelerations and terms of horizontal forces. Accordingly, noises causedby operations of terms of accelerations can be eliminated and real-timeoperations can be easily achieved in the absence of operations of termsof accelerations. In particular, accurate estimation can be carried outwhile the person (1) sitting in and rising from a chair.

[0147] In the embodiment mentioned above, the present invention isapplied to the person (1). The present invention can be applied also tobiped walking robots as biped walking systems. In some biped walkingrobots, the hip and the chest are integrated. In such cases a gyroscopicsensor and a accelerometer for the horizontal direction are attached toeither the hip or the chest alone to estimate ground reaction forces andjoint moments on the legs in a similar way to that of theabove-mentioned embodiment. Further, in biped waking robots, bendingangles of the hip joints and the knee joints can be obtained throughcontrolled variables of control devices for joint actuators.

[0148] In the embodiment mentioned above, data detected by the hipvertical accelerometer (21) are directly used to determine a phase ofmotions of the legs (2). In place of the detected data, for example, thevertical component of acceleration a0 of the hip (3) in the absolutecoordinate system Cf, obtained by the reference-acceleration measuringmodule (28), can be used.

[0149] As mentioned above, according to the present invention, jointmoments acting on the legs of walking systems can be obtained andtorques to be applied to the joints can further be obtained, in controlof human assist systems and in control of movement of biped walkingrobots. Such human assist systems are intended to assist humanoperations against gravity including going up and down stairs, sittingand standing up, squatting, and moving up and down with heavy load.

What is claimed is:
 1. A method for obtaining torques to be applied tojoints of a leg of a biped walking system, comprising the steps of:determining which leg or legs are in contact with the ground; obtainingthe vertical component of a ground reaction force acting on the leg,based on which leg or legs are in contact with the ground; obtaining apoint of application of the ground reaction force; obtaining momentsacting around the joints of the leg, using the vertical component of theground reaction force acting on the leg at the point of application ofthe ground reaction force, the vertical components of forces acting onthe joints of the leg and a term of the acceleration of gravity andwithout using the horizontal components of the forces acting on thejoints of the leg and a term of acceleration except the term of theacceleration of gravity; and obtaining the torques to be applied to thejoints of the leg, based on the moments acting around the joints of theleg.
 2. A method according to claim 1, wherein in a single-support modethe vertical component of the ground reaction force acting on the leg isassumed to be M·g and in a double-support mode the vertical component ofthe ground reaction force acting on each of the legs is assumed to be(½)·M·g, where M is a weight of a person and g is the acceleration ofgravity.
 3. A method according to claim 1 or 2, wherein in the step ofdetermining which leg or legs are in contact with the ground, thedetermination is made based on a value of the vertical component ofacceleration measured on the body.
 4. A method according to claim 1 or2, in the step of determining which leg or legs are in contact with theground, the determination is made using a sensor.
 5. A method accordingto any one of claims 1 to 4, wherein in the step of obtaining a point ofapplication of the ground reaction force, the point is obtained based onthe attitude of the leg and a location of the center of gravity of thebody.
 6. A method according to claim 5, wherein in the step of obtaininga point of application of the ground reaction force, the point isobtained further using information from a sensor.
 7. A method accordingto any one of claims 1 to 6, in the step of obtaining moments actingaround the joints of the leg, at first the vertical component of a forceacting on and a moment acting around the knee joint of the shin, areobtained using the vertical component of the ground reaction forceacting on the shin at the point of application of the ground reactionforce and a term of the acceleration of gravity and without using thehorizontal component of the ground reaction force and a term ofacceleration except the term of the acceleration of gravity and then thevertical component of a force acting on and a moment acting around thehip joint of the thigh, are obtained using the vertical component of aforce acting on and a moment acting around the knee joint of the thighand a term of the acceleration of gravity and without using thehorizontal component of the horizontal component of the force acting onthe knee joint and a term of acceleration except the term of theacceleration of gravity.
 8. A method for obtaining moments acting aroundjoints of a leg of a biped walking system, comprising the steps of:determining which leg or legs are in contact with the ground; obtainingthe vertical component of a ground reaction force acting on the leg,based on which leg or legs are in contact with the ground; obtaining apoint of application of the ground reaction force; and obtaining themoments acting around the joints of the leg, using the verticalcomponent of the ground reaction force acting on the leg at the point ofapplication of the ground reaction force, the vertical components offorces acting on the joints of the leg and a term of the acceleration ofgravity and without using the horizontal components of the forces actingon the joints of the leg and a term of acceleration except the term ofthe acceleration of gravity.
 9. A processor for obtaining torques to beapplied to joints of a leg of a biped walking system, the processorbeing operable in association with angular sensors on the joints and atleast one sensor set on the body of the biped walking system, whereinthe processor is configured to perform the steps of: determining whichleg or legs are in contact with the ground, using information from theat least one sensor set on the body; obtaining an attitude of the leg,using information from the angular sensors; obtaining a location of thecenter of gravity of the whole body including the leg; obtaining thevertical component of a ground reaction force acting on the leg, basedon which leg or legs are in contact with the ground; obtaining a pointof application of the ground reaction force, using the attitude of theleg and the location of the center of gravity of the whole body;obtaining moments acting around the joints of the leg, using thevertical component of the ground reaction force acting on the leg at thepoint of application of the ground reaction force, the verticalcomponents of forces acting on the joints of the leg and a term of theacceleration of gravity and without using the horizontal components ofthe forces acting on the joints of the leg and a term of accelerationexcept the term of the acceleration of gravity; and obtaining thetorques to be applied to the joints of the leg, based on the momentsacting around the joints of the leg.
 10. A processor for obtainingtorques to be applied to joints of a leg of a biped walking system, theprocessor being operable in association with angular sensors on thejoints, at least one sensor set on the body of the biped walking systemand at least one sensor set on the leg, wherein the processor isconfigured to perform the steps of: determining which leg or legs are incontact with the ground, using information from the at least one sensorset on the leg; obtaining an attitude of the leg, using information fromthe angular sensors; obtaining a location of the center of gravity ofthe whole body including the leg; obtaining the vertical component ofacceleration of the center of gravity of the whole body including theleg, using information from the at least one sensor set on the body;obtaining the vertical component of a ground reaction force acting onthe leg, based on which leg or legs are in contact with the ground, theattitude of the leg, the location of the center of gravity of the wholebody and the vertical component of acceleration of the center of gravityof the whole body; obtaining a point of application of the groundreaction force, using the attitude of the leg and the location of thecenter of gravity of the whole body; obtaining moments acting around thejoints of the leg, using the vertical component of the ground reactionforce acting on the leg at the point of application of the groundreaction force, the vertical components of forces acting on the jointsof the leg and a term of the acceleration of gravity and without usingthe horizontal components of the forces acting on the joints of the legand a term of acceleration except the term of the acceleration ofgravity; and obtaining the torques to be applied to the joints of theleg, based on the moments acting around the joints of the leg.
 11. Aprocessor for obtaining moments acting around joints of a leg of a bipedwalking system, the processor being operable in association with angularsensors on the joints, at least one sensor set on the body of the bipedwalking system, wherein the processor is configured to perform the stepsof: determining which leg or legs are in contact with the ground, usinginformation from the at least one sensor set on the body; obtaining anattitude of the leg, using information from the angular sensors;obtaining a location of the center of gravity of the whole bodyincluding the leg; obtaining the vertical component of acceleration ofthe center of gravity of the whole body including the leg, usinginformation from the at least one sensor set on the body; obtaining thevertical component of a ground reaction force acting on the leg, basedon which leg or legs are in contact with the ground; obtaining a pointof application of the ground reaction force, using the attitude of theleg and the location of the center of gravity of the whole body; andobtaining the moments acting around the joints of the leg, using thevertical component of the ground reaction force acting on the leg at thepoint of application of the ground reaction force, the verticalcomponents of forces acting on the joints of the leg and a term of theacceleration of gravity and without using the horizontal components ofthe forces acting on the joints of the leg and a term of accelerationexcept the term of the acceleration of gravity.
 12. A processor forobtaining moments acting around joints of a leg of a biped walkingsystem, the processor being operable in association with angular sensorson the joints, at least one sensor set on the body of the biped walkingsystem and at least one sensor set on the leg, wherein the processor isconfigured to perform the steps of: determining which leg or legs are incontact with the ground, using information from the at least one sensorset on the leg; obtaining an attitude of the leg, using information fromthe angular sensors; obtaining a location of the center of gravity ofthe whole body including the leg; obtaining the vertical component ofacceleration of the center of gravity of the whole body including theleg, using information from the at least one accelerometer; obtainingthe vertical component of a ground reaction force acting on the leg,based on which leg or legs are in contact with the ground; obtaining apoint of application of the ground reaction force, using the attitude ofthe leg and the location of the center of gravity of the whole body; andobtaining the moments acting around the joints of the leg, using thevertical component of the ground reaction force acting on the leg at thepoint of application of the ground reaction force, the verticalcomponents of forces acting on the joints of the leg and a term of theacceleration of gravity and without using the horizontal components ofthe forces acting on the joints of the leg and a term of accelerationexcept the term of the acceleration of gravity.